Posts Tagged ‘EMC’

BRL Test is committed to being your one stop shop for EMC equipment.  Ophir RF amplifiers  have been trusted by theBRL-TEST EMC community since 1992.   Products range in frequency from 10 kHz to 18 GHz, with power levels from 1 Watt to 24 kilowatts. Made in the USA.  Multi year warranties are a testiment to their quality construction and longevity.

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AH118 Compower

BRL Test is your EMC EMI Headquarters. Click for Com-Power AH-118 pricing now.

Com-Power AH-118

Click here for datasheet and quoteform at BRLTest.com  Call BRL Test today at 407-682-4228

The Horn antenna Model AH-118 is a standard broadband double ridged waveguide horn antenna. This antenna is linearly polorized and is designed specifi cally for EMC measurements for the 1-18 GHz frequency range. The AH-118 Horn antenna can be used for emissions and immunity testing. The gain of this Horn antenna is at least 6.1 dBi over the entire frequency range. Model AH-118 can accept up to 300 Watts input power in continuous mode. This antenna is constructed using light weight aluminum with a corrosion resistant conductive coating. The mounting base of Model AH-118 has 1/4 inch x 20 threads. This allows the antenna to be mounted on a tripod (Model AT-100) or a tripod with matching threads. Each antenna is individually calibrated at 3 meters. The calibration data and certifi cate will be shipped with each antenna.

This antenna is suitable for ANSI 63.4, CISPR16, EN 55022, FAA and other EMC standards that require emissions and immunity testing. The high gain reduces input power requirements to generate high electromagnetic field levels for immunity testing. High gain also increases antenna sensitivity to low level signals. During emissions measurement, the fi eld strength (dBV/m) is calculated by adding the antenna factor (dB/m) to the voltage measured (dBV) at the antenna terminals. For immunity testing, the input power requirement P in Watts to generate E Electric Field Strength in V/m at a distance in D meters can be calculated by using the following formula: P = E2 x D2 / 30 x Numeric Gain G = 20 log F -29.79- AF G = 10 log (Numeric Gain) Where G= gain in dBi F = Frequency in MHz AF = antenna factor in dB

Frequency Range: 1 GHz – 18 GHz Input Power: 300 Watts continious VSWR: 2.0 : 1 Polorization: Linear Impedance: 50 Ω Connector type: N Female Weight: 4 lb. max. Size: 7.8″ X 9.5″ X 5.6″ max.

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   Turntables for EMC EMI

-July 19, 2013 in EDN

Questions on EMC pre-compliance testing for radiated emissions

Questions on EMC pre-compliance testing for radiated emissions

Thanks for all the great questions presented following my recent EMC webinar, sponsored byRohde & Schwarz and hosted by UBM TechOnline. If you missed the webinar, you may go here to download a copy of the slides and listen to the webinar “on-demand”. As I mentioned in the previous two postings, I’ve grouped them by topic and will be answering them all the best I can. Be advised that for many questions pertaining to EMC, the best answer is, “it depends”, so there may not be one answer for all cases. I’ll try to include my assumptions in the answers. The questions have been edited for clarity.

This posting will address questions on Pre-Compliance Testing for Radiated Emissions.

Q. Most folks don’t have access to a semi-anechoic chamber. Any recommendations for the room used for radiated pre-compliance tests?

A. True…most semi-anechoic chambers are very expensive. I’ve been very successful using conference rooms (or better) basements to set up a simple 3m measurement range for confirming pass/fail data. Of course, I like to give myself about 6 dB of margin, just to lower the risk of failing in a real chamber.

Here is one major issue: Ambient signals (that is, signals from external sources like AM & FM broadcast, television, two-way radios, military transmitters and mobile phone and wireless communications) can mask the harmonics from the product, unless you can test in a shielded room. Making the measurement in a rural area or basement can help. Knowing where the major emissions lie is important, because you can then narrow down the span to include just that harmonic. If the harmonic in question is still being masked by an ambient signal, often, you can narrow down the resolution bandwidth (assuming the harmonic is a narrow band “CW” signal) and make an approximate amplitude measurement.

Another issue is that very strong ambient signals, say from a nearby FM broadcast or television station, can overload the front end of the EMI receiver (to some degree, depending on whether it has preselection filters) or spectrum analyzer. Because spectrum analyzers have very wideband front end circuitry, a signal that overloads the analyzer can affect (compress) the other measured signal amplitudes.

You’ll also need to know the system losses and gains, so you can calculate the voltage at the antenna terminals. This would include coax loss, attenuator losses (if used), preamp gain (if used), and the antenna factor (provided by the antenna manufacturer).

Q. The equipment you show is for pre-compliance or to resolve a problem. For EMC full compliance, which are the advices you give in order to comply with the tests?

A. You really have two choices; assemble the equipment and semi-anechoic chamber required to perform your own radiated emissions testing (can cost $500k to $3M, depending on 3m or 10m chamber), or have a third-party test facility run the compliance testing for you. Unless your company is willing to fund such a project, my advice is to rely on an outside test lab.

Q. How to setup pre-compliance test lab, what are minimum possible equipments required with limited budget?

A. If your budget is limited, the minimum equipment required is a good spectrum analyzer ($2 to $20k), an EMI antenna (or antennas) that can tune from at least 30 to 1000 MHz (however, the U.S. FCC can require testing up to 6 GHz, or more), a turntable to set up the product with its attached cables, and an antenna tower that can be adjusted in height and can turn the antenna from horizontal to vertical polarization. You may also need a preamplifier to boost the signal from the antenna. It’s possible to make a DIY turntable and tower to save a little money. The total cost might run $10k to $50k. Note, also, that the frequency range required also depends on your product family and test standard used. For example, some ITE and medical products require measurement all the way to 30 GHz, which could double those costs.

Q. If you use a current loop probe to measure the dBuA on a spectrum analyzer and calculate the current for differential-mode currents, do you still need to input the L & s of the formula you mentioned to calculate E field?

A. Yes, you do. An estimate works OK. The main thing is to capture the length of the circuit trace or cable.

Q. CM and DM calculations – where did the constant come from? How was it derived?

A. These are derived in Dr. Clayton Paul’s book, Introduction to Electromagnetic Compatibility (2nd ed.) starting on page 509 (Differential-Mode Current Emission Model) through page 516 (Common-Mode Current Emission Model). Assuming we start with the Hertzian dipole model, the DM and CM constants are comprised of the intrinsic impedance of free space, phase constant and a factor of 2*PI or 4*PI.

Q. Why is conducted emission’s maximum frequency 152 MHz?

A. I don’t recall mentioning 152 MHz, however, generally speaking, common-mode emissions start to decrease around 200 to 300 MHz as a dominant factor in harmonics. That’s not saying that CM currents don’t exist above that frequency – just that they aren’t the dominant source.

Q. Could you use that scope connected to an antenna for wide band radiated emissions?

A. Interesting question, as most designers have access to oscilloscopes, rather than spectrum analyzers. As well, most digitizing scopes also have FFT functions. The answer is it depends a lot on the sensitivity of the scope in question. Most scopes can’t measure accurately below a few mV and the signal levels at the antenna terminals might be in the uV region. So, unless your scope can measure down to the uV level, it probably won’t work well. Some of the newer scopes from Rhode & Schwarz and LeCroy have sensitivities in the uV, however, so they might be worth a try. However, you’ll miss out on the convenience of dedicated spectrum analyzer controls, of which there are many. If cost is an issue, you might check out the Rigol DSA815 analyzer that I reviewed recently.

Q. How accurate are FFT readings from a oscilloscope using regular oscilloscope probes compared to near-field probes?

A. Hard to say, as most near-field probes aren’t really calibrated. Now, if the question is really, “Can I perform troubleshooting with either near-field probes or scope probes”, the answer is “yes”. The other part of your question relates to the accuracy of the FFT data on a scope. I would have to say, most of the newer scopes will be fairly accurate, however input sensitivity and internally generated noise in the front end will come in to play and mask very small signals. It’s important that the scope have the ability to be adjusted to a resolution bandwidth of 100 to 120 kHz (for the 30 to 1000 MHz band) in order to compare accurately with spectrum analyzer measurements. But consider the discussion above, as well.

I have written extensively on how to perform pre-compliance testing for radiated emissions and would invite you all to read some of the postings here on The EMC Blog, as well as the links to some of my articles in other magazines.

Feel free to add additional questions related to PC boards. I’ll be posting additional questions asked during this webinar in later blogs. If you missed the webinar, you may go here to download a copy of the slides and listen to the webinar “on-demand”.

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BRL Test is your EMC EMI Headquarters

CGO-505 Comb Generator

CGO-505 Comb Generator 5 MHz Step,1.5 GHz Com Power.  BRL Test is your EMC EMI Headquarters.

EMC Site testing is a snap when you verify with this state of the art comb generator.  The CGO-505 is 5 MHz Step,1.5 GHz.  BRL Test is your EMC EMI headquarters.  Click here to compare Comb Generators at BRLTest.com.  Call your BRL Test Representative today at 866-275-8378

CGO-501 and CGO-505 Comb Generators are a broadband EMC signal source for quick EMC site testing. They radiate signals up to 1500 MHz.  EMC labs calibrate their radiated emissions test sites, instrumentation and accessories at least once a year. The calibration procedures are elaborate and time consuming. However, calibration does not prevent equipment malfunction in between calibration period such as damaged receivers,, broken cables, poor connections, bad antenna, etc. Monitoring a few frequencies regularly on the Comb Generator’s broadband radiated output can verify the entire setup quickly and efficiently. Any potential problems with the test setup can be detected before it causes erroneous results. It is powered by a rechargeable NimH battery pack. It has circular shape for more uniform radiated output.  BRL Test is an authorized Com-Power Dealer.